Post on 06-Apr-2022
University of Central Florida University of Central Florida
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Honors Undergraduate Theses UCF Theses and Dissertations
2016
Quantifying The Success Of Eastern Oyster Pilot Reefs In Brevard Quantifying The Success Of Eastern Oyster Pilot Reefs In Brevard
County, Florida County, Florida
Lacie Anderson University of Central Florida
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Evolutionary Biology Commons
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Recommended Citation Recommended Citation Anderson, Lacie, "Quantifying The Success Of Eastern Oyster Pilot Reefs In Brevard County, Florida" (2016). Honors Undergraduate Theses. 59. https://stars.library.ucf.edu/honorstheses/59
QUANTIFYING THE SUCCESS OF EASTERN OYSTER PILOT REEFS IN BREVARD COUNTY, FLORIDA
by
LACIE L. ANDERSON
A thesis submitted in partial fulfillment of the requirements for the Honors in the Major Program in Biology
in the College of Sciences and in the Burnett Honors College at the University of Central Florida
Orlando, Florida
Spring Term, 2016
Thesis Chair: Linda Walters, PhD
ii
ABSTRACT Crassostrea virginica, the eastern oyster, is a native keystone species that
inhabits many coastal and estuarine ecosystems along the Atlantic seaboard.
Introduction of the eastern oyster into estuarine areas with limited current populations is
gaining popularity as a pro-active approach to improve estuarine water quality. In
November 2014 and April 2015, a total of five pilot oyster reef treatments were deployed
in Brevard County: bagged adult oysters (grown by community members under their
docks through oyster gardening) collected in fall 2014 and spring 2015, bagged clean
shell, oyster restoration mats, and empty plots (control). Locations of deployment
included a Merritt Island impoundment (Marsh Harbor), Nicol Park (Port St. John), and
Scout Island (Melbourne Beach). Prior to deployment, we collected morphometric data
(shell length, weight) on all gardened oysters. Abiotic factors including salinity, air and
water temperature, and wind speed were collected monthly. During quarterly sampling
at each site, morphometric data were collected for all live oysters, surviving and newly
recruited. Results show survival of gardened oysters and natural recruitment differed by
and depended greatly on the within-site location of each reef. In areas with no
recruitment and limited gardened oyster survival, regular deployment of gardened
oysters is needed for long term success. In areas with natural recruitment, bagged,
clean shell or oyster restoration mats are most successful. Future restoration sites
should be tested prior to any large-scale oyster deployments.
iii
DEDICATIONS
For my parents, thank you providing me with the opportunity to have a college education and for always being there to support and encourage me.
For my professors, thank you for encouraging me to go above and beyond the classroom.
iv
ACKNOWLEDGEMENTS
I would like to thank CEE Lab members, Brevard Zoo, volunteers and Brevard County Natural Resources for field assistance; the residents of Brevard County who
participated in oyster gardening; Paul Sacks for assistance in the field and site map illustrations; Dr. Melinda Donnelly and Panayoita Makris for GIS and analysis help. I
would like to thank UCF Department of Biology, Brevard County, FL Dept. of Environmental Protection, Office of Undergraduate Research, LEAD Scholars and
SURF for funding this project. Special thanks to my thesis chair Dr. Linda Walters for always encouraging me and providing me with the opportunity to be the lead on this
research project. Thank you Dr. Melinda Donnelly and Dr. Kelly Kibler for serving on my committee and providing me with meaningful insight.
v
TABLE OF CONTENTS CHAPTER 1: INTRODUCTION ......................................................................... 1
Estuaries ...................................................................................................................... 1
Oysters ........................................................................................................................ 1
Indian River Lagoon ..................................................................................................... 2
Pilot Oyster Reefs ........................................................................................................ 3
CHAPTER 2: METHODS ................................................................................. 5
Site Selection ............................................................................................................... 5
Live Oyster Collection .................................................................................................. 7
Reef Construction ........................................................................................................ 7
Data Collection ........................................................................................................... 11
Data Analysis ............................................................................................................. 12
CHAPTER 3: RESULTS ................................................................................. 14
Number and Size of Oysters ...................................................................................... 15
Live Oyster Weight ..................................................................................................... 23
Natural Recruitment ................................................................................................... 25
Abiotic Factors ........................................................................................................... 26
CHAPTER 4: DISCUSSION ............................................................................ 29
Number and Size of Oysters ...................................................................................... 29
Live Oyster Weight ..................................................................................................... 31
Natural Recruitment ................................................................................................... 32
Abiotic Factors ........................................................................................................... 33
Restoration Implications ............................................................................................. 33
REFERENCES ............................................................................................. 35
vi
LIST OF FIGURES Figure 1 Map of pilot reef study sites. ............................................................................. 6
Figure 2 Cross section and overview of pilot oyster reef layout. ..................................... 8
Figure 3 Cross section of a pilot reef constructed from bags. ......................................... 9
Figure 4 Aerial view of a pilot reef constructed from bags. ............................................. 9
Figure 5 Aerial view of a pilot reef constructed from mats. ............................................. 9
Figure 6 Oyster bag dimensions. .................................................................................. 10
Figure 7 Oyster mat dimensions. .................................................................................. 11
Figure 8 Mean number of live oysters per bag for Nicol Park. FA= fall adult oyster
treatment, SP= spring adult oyster treatment, and BL= blank shell treatment. 1, 2, and 3
refer to the reef replicates. ............................................................................................ 17
Figure 9 Mean number of live oysters per bag for Marsh Harbor. FA= fall adult oyster
treatment, SP= spring adult oyster treatment, and BL= blank shell treatment. 1, 2, and 3
refer to the reef replicates. ............................................................................................ 18
Figure 10 Mean number of live oysters per bag for Scout Island. FA= fall adult oyster
treatment, SP= spring adult oyster treatment, and BL= blank shell treatment. 1, 2, and 3
refer to the reef replicates. ............................................................................................ 19
Figure 11 Mean shell length of live oysters per bag for Nicol Park. FA= fall adult oyster
treatment, SP= spring adult oyster treatment, and BL= blank shell treatment. 1, 2, and 3
refer to the reef replicates. ............................................................................................ 20
vii
Figure 12 Mean shell length of live oysters per bag for Marsh Harbor. FA= fall adult
oyster treatment, SP= spring adult oyster treatment, and BL= blank shell treatment. 1, 2,
and 3 refer to the reef replicates. .................................................................................. 21
Figure 13 Mean shell length of live oysters per bag for Scout Island. FA= fall adult
oyster treatment, SP= spring adult oyster treatment, and BL= blank shell treatment. 1, 2,
and 3 refer to the reef replicates. .................................................................................. 22
Figure 14 Summary of mean total live oyster weight per bag for each reef during the fall
2015 sampling. ‘FALL’ refers to fall adult oyster treatment, ‘SPRING’ refers to spring
adult oyster treatment, and ‘BLANK’ refers to blank shell bag treatment. There was a
significant interaction between SITE:TREATMENT:REEF (p<0.001). ........................... 24
Figure 15 Comparison of number of oysters for blank shell bag (‘BLANK’) and
restoration mat (‘MAT’) treatments. The numbers 1, 2, & 3 refer to the reef replicates.
There was a significant TREATMENT:REEF interaction (p<0.001). ............................. 26
viii
LIST OF TABLES
Table 1 Summary of initial morphometric data on fall gardened live oysters for each site
represented by the means of each reef. Initial mean weight represents the mean of the
total live oyster weight per bag. ..................................................................................... 14
Table 2 Summary of initial morphometric data on spring gardened live oysters for each
site represented by the means of each reef. Initial mean weight represents the mean of
the total live oyster weight per bag. ............................................................................... 15
Table 3 Results for overall four-factor MANOVA. ......................................................... 16
Table 4 Overall 3-way ANCOVA comparing final live oyster weight versus initial live
oyster weight. ................................................................................................................ 23
Table 5 Overall MANOVA of recruitment on oyster bags versus oyster mats. .............. 25
Table 6 Abiotic data collected. There is significant variation by date (p=0.001) and slight
significant variation by site (p=0.03). ............................................................................. 26
Table 7 MANOVA summary model, all abiotic factors considered. ............................... 28
1
CHAPTER 1: INTRODUCTION
Estuaries Estuaries are semi-enclosed water bodies whose tides are driven by the influx of
seawater from the neighboring ocean (Cain et al. 2011). The salinity in estuaries is
generally lower than that of the open ocean due to the inflow of freshwater from
connecting rivers and streams (Dybas 2002). Estuaries contain a mix of sediment
sources and transport processes, which represent both fluvial and marine sources
(Dalrymple et al. 1992). Estuaries are some of the most biologically productive coastal
ecosystems in the world (Taylor 2012). The high productivity in estuarine ecosystems is
a result of the high nutrient availability, which forms as a result of the mixing of
freshwater and saltwater (Cain et al. 2011). Phytoplankton, the primary producers in
estuaries, are able to thrive when large amounts of nutrients are available (Odebrecht et
al. 2015). Many species of fish, birds, and amphibians rely on estuaries as a nursery,
which provides them with abundant shelter and food (Dybas 2002). Shellfish of many
different species, which can be found in estuaries, are capable of naturally improving
the quality of ecosystems through many different processes.
Oysters Oysters are ecosystem engineers and can be found in estuaries around the
world. The reef structures oysters form provide habitat for many different ecologically
important species in coastal ecosystems (Beck et al. 2011, Drexler et al. 2014). Oysters
also perform other important ecological functions, such as providing food to other
2
important species, transferring nutrients from the water to organisms that inhabit the
seabed, and preventing eutrophic water conditions (Drexler et al. 2014). Estuarine
ecosystem degradation and overharvesting have had detrimental effects on oyster reef
ecological functions (Beck et al. 2011).
Crassostrea virginica, the eastern oyster, is a native keystone species that
inhabits many coastal and estuarine ecosystems in the state of Florida, including the
Indian River Lagoon. The eastern oyster provides habitat for other species and is also
an indicator of water quality in estuaries along the Atlantic and Gulf coasts of Florida
(Drexler et al. 2014). One adult eastern oyster is capable of filtering up to 189 liters of
water in a day (Jackson 2014). Through their filtration, eastern oysters are able to
remove particles from the water column, which ultimately may increase light penetration
providing improved habitat for submerged vegetation such as seagrass (Volety et al.
2014). By improving water quality parameters and increasing the amount of marine
vegetation, oysters are capable of altering the structure and quality of an entire
ecosystem.
Indian River Lagoon The Indian River Lagoon, a biologically diverse estuary, extends along Florida’s
eastern seaboard over 240 kilometers (Hanisak et al. 2015). Due to its unique
properties, such as large size and high biodiversity, the Indian River Lagoon has been
deemed an “Estuary of National Significance” (Taylor 2012). Unfortunately, the Indian
River Lagoon faces many threats, which are often human-caused (Hanisak et al. 2015).
3
For example, a loss of 75-90% of the historical saltmarsh and mangroves surrounding
the estuary, due to filling and impounding, has led to a decrease in water quality and
fisheries (Dybas 2002, Taylor 2012).
In the Indian River Lagoon efforts have already been made, by Dr. Linda Walters
and colleagues, to conserve and restore natural eastern oyster populations in order to
improve the overall quality of the estuary (Walters 2014). With an increase of human
developments along the coastline of Florida, there is a growing demand to use natural
methods to help maintain and conserve estuarine ecosystems. In many coastal areas
growing amounts of human activity have led to increased nitrogen content in the water.
Using shellfish has been proposed as an inexpensive, environmentally friendly
approach to increase denitrification processes and improve water quality (Kellogg et al.
2014). It is for their many important contributions to the ecosystem that the eastern
oyster is being introduced and reintroduced into certain areas to help reverse the effects
of human-caused disturbance.
Pilot Oyster Reefs For this project, University of Florida, Brevard Zoo, and Brevard County Natural
Resources have combined efforts to place the eastern oyster along three segments of
Indian River Lagoon shoreline in Brevard County. Live adult oysters used in this study
were raised (“gardened”) by Brevard County homeowners in suspended habitats under
their docks on the Indian River Lagoon. Residents who participated in oyster gardening
received oysters as spat (juvenile oysters) on oyster shell and raised them for 6-9
4
months in their habitats. Through their engagement with this citizen science project,
Brevard County residents who participated in oyster gardening were educated about the
benefits that oysters provide in the lagoon through free classes offered by Brevard Zoo.
Brevard county residents gardened over 10,000 live oysters that were used in the pilot
oyster reefs for this study. Given the lack of oysters on the shorelines of the Indian River
Lagoon in Brevard County, placing of oysters to these areas, if successful, may
ultimately improve local water quality and marine wildlife habitat.
My research focuses on quantifying the success of the pilot oyster reefs
deployed in Brevard County. Success will be determined by: 1. Survival of oysters, 2.
Natural recruitment of oysters, and 3. Comparisons of oyster shell length and weight at
each location. This research project was initiated in November 2014 and will continue
until summer 2016. Throughout the study, morphometric data on the pilot oyster reefs
are collected quarterly and abiotic data are collected monthly. Evaluating the success of
these pilot oyster reefs will allow us to determine if these methods were effective for
relocating oysters in the Indian River Lagoon.
5
CHAPTER 2: METHODS
Site Selection Three locations in Brevard County, along Indian River Lagoon shorelines, were
chosen for this study by Brevard County Natural Resources during the summer of 2014
based on: accessibility, county ownership, amount of recreational activity, salinity and
proximity to seagrass. Since Brevard County Natural Resources is the lead on this
project, potential sites were first narrowed down to county-owned properties that were
along the Indian River Lagoon and accessible by car. These properties needed to
provide safe access for transportation of materials and volunteers but also needed to be
remote enough to not be disturbed by the public. After potential sites were visited,
seagrass field surveys undertaken ensured no seagrass was present, due to its
protection in the state of Florida. Following seagrass surveys, historical range of salinity
(10-28ppt) and dissolved oxygen (>4 mg/L), that is optimal for oyster growth and
reproduction, were taken into consideration.
The three final locations selected were Nicol Park (Port St. John), Scout Island
(Melbourne Beach), and a Merritt Island restored salt marsh mosquito impoundment
(Marsh Harbor). Nicol Park is a waterfront public park located along U.S. Highway 1 in
the town of Port St. John. Pilot oyster reefs at this location were accessed directly on
the northern edge of the park. Pilot oyster reefs at the Scout Island location were
accessed via trail within Long Point Park and Campground. The Merritt Island location
was accessed by state vehicle only over private roads. This impoundment separated
6
the Indian River Lagoon from nearby wetlands and was periodically flooded or dried to
reduce salt marsh mosquito reproduction.
Figure 1 Map of pilot reef study sites.
7
Live Oyster Collection Live adult oysters used in this study were gardened (raised from juvenile oysters
on shell) for 6-9 months under docks by Brevard County community members. Live
adult oysters were collected from oyster gardeners in November 2014 and March 2015.
Oyster gardeners brought their live oysters to the county parks located next to each
study site to be collected. The parks used for gardened oyster drop-off and pre-
deployment data collection were: Long Point Park and Campground (Scout Island),
Rotary Park (Marsh Harbor), and Nicol Park (Port St. John). University of Central
Florida researchers, Brevard Zoo staff, and Brevard County Natural Resources staff
sorted through adult oysters collected from oyster gardeners to assure live oysters were
present. Once oysters were sorted they were moved to pre-deployment data collection
and placed into bags.
Reef Construction A total of five treatments were deployed at each location: 1. Control = empty plot,
2. Oyster restoration mats, 3. Bagged blank shell (disarticulated oyster shell only, no
live), 4. Bagged adult gardened oysters collected in fall 2014, and 5. Bagged adult
gardened oysters collected in spring 2015. There were five entire reef replicates of each
treatment type, which resulted in a total of 25 pilot oyster reefs at each site. All pilot
oyster reefs covered a total of 152 meters of shoreline at each location. Three meters
separated each treatment replicate reef.
8
Figure 2 Cross section and overview of pilot oyster reef layout.
Pilot oyster reefs that consisted of oyster bags (fall/spring adult gardened oysters
and bagged clean shell) were built with a total of 48 bags and were approximately 2.7 m
long, 0.5 m high, and 1.8 m wide. Each pilot reef had two layers of shell bags. The
bottom layer consisted of two rows of 12 bags that were filled with clean shell only. This
layer was present to elevate the top layer away from the sediment. The top layer
consisted of two rows of 12 bags; the seaward row of 12 contained the tagged bags
monitored in the study. Top and bottom layers of adjacent oyster bags were bound to
one another with zip ties to prevent movement of bags. Pilot oyster reefs that consisted
of oyster restoration mats were built with a total of 24 mats aligned in four rows of six
mats. Pilot oyster reefs constructed from oyster restoration mats were made
9
approximately 2.74 m across and 1.83 m wide to obtain a footprint similar to bag reefs.
The seaward two rows of six mats were tagged and monitored in the study.
Figure 3 Cross section of a pilot reef constructed from bags.
Figure 4 Aerial view of a pilot reef constructed from bags.
Figure 5 Aerial view of a pilot reef constructed from mats.
10
Oyster bags were constructed using DelStar Technologies “Naltex” nylon net
material that was cut into 1.75 m long tubes. To fill oyster bags, these mesh tube
segments were tied on one side, 0.25 m from end, and fitted over a PVC tube 0.6 m
long and 0.16 m wide. Live oysters and oyster shells, in an 18.9 liter bucket, were
funneled through the PVC tube and into the mesh bag. The PVC tube was then
removed and the oyster bag was tied shut. The same method was used to fill oyster
bags that consisted of only blank shell. Blank shell refers to clean, disarticulated oyster
shells that contain no live oysters. These shells were donated from shucking facilities
where the oyster meat were previously harvested as a food source. All shells were
quarantined for a minimum of three months. Each oyster bag, used in fall and spring
adult gardened oyster treatments, was filled with a mixture of clean shell and 50
gardened live adult oysters. The final shell bags were approximately one meter long.
Oyster bags and oyster restoration mats were each tagged with a unique number.
Figure 6 Oyster bag dimensions.
11
Oyster restoration mats were made of VexarTM plastic mesh segments that were
cut in 0.25 m2 squares. Attached to each mat via zip ties were 36 oyster shells, each
with a single hole drilled near the umbo. Oyster restoration mats were attached with zip
ties to concrete irrigation weights on each corner.
Figure 7 Oyster mat dimensions.
Data Collection At each site prior to deployment, morphometric data were collected on live
oysters. Live oyster shell length was measured with digital or analog calipers in
millimeters and cluster weight was measured with digital balances in grams. Using a
random number generator, three of the five treatment replicate reefs were selected to
be monitored.
Post-deployment morphometric data were collected on all treatments every three
months from November 2014 through spring 2016. For the first two sampling periods
12
(spring 2015 & summer 2015), all tagged bags were monitored and for the third and
fourth sampling periods (fall 2015 & spring 2016) a subset of 9 bags and 18 mats per
treatment were sampled. Due to extremely low survival, zero natural recruitment and
accessibility issues, all monitoring for Marsh Harbor ended in summer 2015.
With the help of University of Central Florida, Brevard Zoo, and community
volunteers, bagged treatment contents were emptied by hand and each live oyster was
measured and weighed. Sorted contents were placed into new bags and the original tag
was placed on the new bag. Shell lengths of oysters that naturally recruited on the
oyster restoration mats were measured with a ruler in millimeters. Oyster restoration
mats were kept in original position if it was low tide or moved on shore while
measurement took place if it was high tide.
Since initial deployment in November 2014, measurements of abiotic factors
(salinity, water temperature, air temperature, and wind speed) were collected monthly.
Salinity was collected with a refractometer and measured in parts per thousand. Water
temperature was collected with HOBO tidbit temperature loggers, which recorded the
temperature in degrees Celsius continuously every 15 minutes, and were replaced
monthly. Air temperature measured in Celsius, and wind speed measured in meters per
second, were both collected using an Osprey anemometer.
Data Analysis For this thesis, all oyster data included in the analyses were collected from
November 2014- November 2015 and all abiotic data were those collected from
13
November 2014-January 2016. All data for this thesis were analyzed with model
selection in R.
Monthly water temperatures used in the analysis were calculated by taking the
mean of all temperatures recorded from one abiotic sample date to the next abiotic
sample date. Wind speed used in the analysis refers to the mean wind speed recorded
at time of sampling. Salinities and air temperatures used in the analysis were the values
recorded at time of sampling.
Oyster weights used in the analysis were the total mass (grams) of live oysters in
an oyster bag. Weights recorded for live oysters during the fall 2015 sampling (final
weight) were compared to the bag’s initial weight when first deployed in either fall 2014
or spring 2015, depending on treatment type. Marsh Harbor was not included in this
analysis since there were no final weights recorded for that site in fall 2015. The control
treatment contained no live oysters during the fall 2015 sampling; therefore it was not
included in this analysis. Weights were not monitored on the restoration mat treatment;
therefore it was not included in this analysis.
To compare differences in the amount of natural recruitment by treatment type at
Scout Island, restoration mats were compared to shell bags. Blank shell bags were the
only bagged treatment that started with zero live oysters, thus were the bagged
treatment chosen for this analysis. All oysters seen on both of these treatments were
naturally recruited.
14
CHAPTER 3: RESULTS
Initial morphometric data were collected on all live oysters deployed at each site
(Tables 1, 2). A 3-factor ANOVA (site x treatment x reef) with initial size as the
response shows a significant SITE:TREATMENT interaction (p<0.001). Oyster shell
length varied by the location in which they were reared and the season during which
they were reared. A 3-factor ANOVA (site x treatment x reef) with initial mass as the
response shows a significant SITE:TREATMENT interaction (p=0.002). Oyster mass
varied by the location in which they were reared and the season during which they were
reared.
Table 1 Summary of initial morphometric data on fall gardened live oysters for each site represented by the means of each reef. Initial mean weight represents the mean of the total live oyster weight per bag.
INITIAL DATA: FALL ADULT OYSTER
TREATMENT
SITE REEF MEAN TOTAL WEIGHT PER
BAG (g)
MEAN SHELL LENGTH (mm)
INITIAL # OYSTERS
SCOUT 1 2460.3 47.14 50
2 2408.4 49.6 50
3 2249.8 46.0 50 NICOL 1 2415.8 43.1 50
2 1935.7 45.4 50
3 2437.3 44.3 50 MARSH 1 798.3 44.2 50
2 1528.6 44.4 50
3 2145.8 48.7 50
15
Table 2 Summary of initial morphometric data on spring gardened live oysters for each site represented by the means of each reef. Initial mean weight represents the mean of the total live oyster weight per bag.
INITIAL DATA: SPRING ADULT OYSTER
TREATMENT
SITE REEF MEAN TOTAL WEIGHT PER
BAG (g)
MEAN SHELL LENGTH (mm)
INITIAL # OYSTERS
SCOUT 1 1569.8 48.5 50
2 1589.9 49.2 50
3 1653.3 47.9 50
NICOL 1 888.1 41.8 50
2 911.5 41.2 50
3 1101.2 43.4 50
MARSH 1 2006.0 53.1 50
2 1281.5 56.9 50
3 1912.9 53.3 50
Number and Size of Oysters An overall four-factor MANOVA (date x site x treatment x reef), combining the
variables of size and number of oysters, which are correlated by bag (replicate),
resulted in a significant interaction between all factors (p<0.001) (Table 3). When the
oysters were sampled, deployment site, whether the treatment started out with live
oysters, and within-site location of the reef, are all factors which influenced the variation
in number and size of oysters found.
16
Table 3 Results of overall four-factor MANOVA.
OVERALL: NUMBER + SIZE Df Pillai
approx. F Num Df Den Df Pr(>F)
DATE 3 0.60181 107.75 6 1502 < 0.001 SITE 2 0.68879 197.25 4 1502 < 0.001 TREATMENT 4 1.33268 374.95 8 1502 < 0.001 REEF 2 0.48541 120.34 4 1502 < 0.001 DATE:SITE 6 0.60448 54.22 12 1502 < 0.001 DATE:TREATMENT 7 0.05912 3.27 14 1502 < 0.001 SITE:TREATMENT 8 1.11226 117.62 16 1502 < 0.001 DATE:REEF 6 0.33074 24.8 12 1502 < 0.001 SITE:REEF 4 0.59202 78.94 8 1502 < 0.001 TREATMENT:REEF 8 0.85322 69.84 16 1502 < 0.001 DATE:SITE:TREATMENT 11 0.11829 4.29 22 1502 < 0.001 DATE:SITE:REEF 12 0.44285 17.8 24 1502 < 0.001 DATE:TREATMENT:REEF 14 0.05226 1.44 28 1502 0.06465 SITE:TREATMENT:REEF 16 0.8757 36.56 32 1502 < 0.001 DATE:SITE:TREATMENT:REEF 22 0.12641 2.3 44 1502 < 0.001 Residuals 751
A four-factor ANOVA (date x site x treatment x reef) with number of oysters as
the response variable shows a significant interaction between all factors (p<0.001)
(Figures 8, 9, 10). This indicates number of oysters present is strongly influenced by
sampling date, deployment site, whether the treatment started with live oysters, and the
reef’s within-site location. A four-factor ANOVA (date x site x treatment x reef) with
oyster size as the response variable shows a significant interaction between all factors
(p=0.003), which seemed to be driven by a strong TREATMENT:REEF interaction
(p<0.001) (Figure 9). This indicates that size of oysters is dependent upon whether the
treatment started out with adult oysters and within-site location of the reef.
17
Figure 8 Mean number of live oysters per bag for Nicol Park. FA= fall adult oyster treatment, SP= spring adult oyster
treatment, and BL= blank shell treatment. 1, 2, and 3 refer to the reef replicates.
18
Figure 9 Mean number of live oysters per bag for Marsh Harbor. FA= fall adult oyster treatment, SP= spring adult
oyster treatment, and BL= blank shell treatment. 1, 2, and 3 refer to the reef replicates.
19
Figure 10 Mean number of live oysters per bag for Scout Island. FA= fall adult oyster treatment, SP= spring adult
oyster treatment, and BL= blank shell treatment. 1, 2, and 3 refer to the reef replicates.
20
Figure 11 Mean shell length of live oysters per bag for Nicol Park. FA= fall adult oyster treatment, SP= spring adult
oyster treatment, and BL= blank shell treatment. 1, 2, and 3 refer to the reef replicates.
21
Figure 12 Mean shell length of live oysters per bag for Marsh Harbor. FA= fall adult oyster treatment, SP= spring
adult oyster treatment, and BL= blank shell treatment. 1, 2, and 3 refer to the reef replicates.
22
Figure 13 Mean shell length of live oysters per bag for Scout Island. FA= fall adult oyster treatment, SP= spring adult
oyster treatment, and BL= blank shell treatment. 1, 2, and 3 refer to the reef replicates.
23
Live Oyster Weight Oyster weight was analyzed with a three-factor ANCOVA (site x reef x
treatment). The summary model consisted of initial weight as the covariate and final
weight as the response. There was a significant interaction between all factors
SITE:TREATMENT:REEF (p<0.001). Change in live oyster weight over time was
influenced by deployment site, whether the treatment started with live oysters, and
within-site location of the reef. These factors influenced the survival and natural
recruitment of oysters, which effected the total mass of oysters present.
Table 4 3-way ANCOVA comparing final live oyster weight versus initial live oyster weight.
Df Sum Sq Mean Sq F value Pr(>F)
INITIAL WEIGHT 1 104473885 104473885 139.81 < 0.001 SITE 1 477148518 477148518 638.52 < 0.001 TREATMENT 2 65913597 32956799 44.1 < 0.001 REEF 2 131776627 65888313 88.17 < 0.001 SITE:TREATMENT 2 304640267 152320134 203.84 < 0.001 SITE:REEF 2 110741983 55370992 74.1 < 0.001 TREATMENT:REEF 4 144830636 36207659 48.45 < 0.001 SITE:TREATMENT:REEF 4 151377889 37844472 50.64 < 0.001 Residuals 33 24659789 747266
24
Figure 14 Summary of mean total live oyster weight per bag for each reef during the fall 2015 sampling. ‘FALL’ refers to fall adult oyster treatment, ‘SPRING’ refers to spring adult oyster treatment, and ‘BLANK’ refers to blank shell bag
treatment. There was a significant interaction between SITE:TREATMENT:REEF (p<0.001).
25
Natural Recruitment To compare the amount of natural recruitment between the restoration mat and
blank shell bag treatments at Scout Island (only site with natural recruitment), a three-
factor MANOVA was performed (Table 5). In this test, size and number of oysters were
combined, which were assumed to be associated by bag or mat (replicate). In the
summary model there was a significant TREATMENT:REEF interaction (p<0.001). This
indicates number and size of naturally recruited oysters is influenced by treatment type
and within-site location of the reef. On a separate three-factor ANOVA with oyster
number as the response there was a significant DATE:TREATMENT:REEF interaction
(p=0.04). When a three-factor ANOVA was ran with oyster size as the response there
were no significant differences. This indicates the significant DATE:TREATMENT:REEF
interaction from the three-factor ANOVA ,with oyster number as the response, is likely
driving the significance of the TREATMENT:REEF interaction in the overall MANOVA.
Table 5 Overall MANOVA of natural recruitment on oyster bags versus oyster mats.
Df
Pillai approx F
num Df
den Df Pr(>F)
DATE 1 0.61928 66.692 2 82 < 0.001
TREATMENT 1 0.88347 310.835 2 82 < 0.001
REEF 2 0.84956 30.646 4 166 < 0.001
DATE:TREATMENT 1 0.11093 5.115 2 82 0.008
DATE:REEF 2 0.30687 7.522 4 166 < 0.001
TREATMENT:REEF 2 0.83042 29.466 4 166 < 0.001
DATE:TREATMENT:REEF 2 0.07942 1.716 4 166 0.149
Residuals 83
26
Abiotic Factors Table 6 Abiotic data collected. There is significant variation by date (p=0.001) and site (p=0.03).
DATE SITE SALINITY (PPT) AIR TEMP °C
AVG WIND (m/s)
AVG WATER TEMP (°C)
12/14/14 SCOUT 25.0 12.1 2.2 20.4 12/14/14 MARSH 24.0 16.0 1.1 20.2 12/14/14 NICOL 22.0 18.3 0.9 19.9 01/16/15 SCOUT 25.0 14.8 4.2 20.6 01/16/15 MARSH 24.0 15.9 1.7 20.5 01/16/15 NICOL 21.0 14.6 2.3 21.2 02/13/15 SCOUT 24.0 13.8 4.2 17.3 02/13/15 MARSH 25.0 16.8 2.3 18.5 02/13/15 NICOL 23.0 13.9 2.6 18.8 03/27/15 SCOUT 31.0 24.6 0.98 22.1
Figure 15 Comparison of number of oysters for blank shell bag (‘BLANK’) and restoration mat (‘MAT’) treatments. The numbers 1, 2, & 3 refer to the reef replicates. There was a significant TREATMENT:REEF interaction (p<0.001).
27
03/27/15 MARSH 23.0 26.6 1.8 22.4 03/27/15 NICOL 22.0 28.9 0.63 22.4 04/24/15 SCOUT 28.5. 26.2 3.2 26.5 04/24/15 MARSH 23.0 29.8 0.93 27.1 04/24/15 NICOL 22.0 30.7 2.1 27.3 05/19/15 SCOUT 31.0 30.7 0.63 27.6 05/19/15 MARSH 22.0 27.3 4.1 27.5 05/19/15 NICOL 23.0 27.0 2.7 28.6 06/12/15 SCOUT 29.0 31.6 0.58 29.6 06/12/15 MARSH 19.0 32.2 1.4 29.2 06/12/15 NICOL 22.0 29.0 2.3 29.6 06/29/15 MARSH 20.0 36.0 0.63 30.3 07/01/15 NICOL 21.0 36.5 1.2 33.0 07/07/15 SCOUT 29.0 31.2 1.8 31.4 08/21/15 NICOL 21.0 34.2 0.58 31.7 08/21/15 SCOUT 22.0 35.0 1.7 29.7 09/27/15 NICOL 22.0 28.2 1.3 31.3 09/27/15 SCOUT 12.0 30.1 1.2 29.8 10/29/15 NICOL 23.0 29.6 0.23 25.9 10/29/15 SCOUT 27.0 28.5 1.6 25.7 11/19/15 NICOL 23.0 29.1 0.98 27.7 11/19/15 SCOUT 23.0 23.5 1.9 26.3 12/28/15 NICOL 25.0 27.2 5.2 23.2 12/28/15 SCOUT 27.0 30.0 0.63 23.2 01/29/16 NICOL 27.0 18.5 1.5 19.4 01/29/16 SCOUT 24.0 17.1 3.6 18.9
Abiotic data were analyzed with an overall two-factor MANOVA (date x site)
combining salinity, air temperature, water temperature, and mean wind speed; this
assumed all factors are correlated spatially by site. There was significant variation by
date (p=0.001) and by site (p=0.03) (Table 7). On a separate ANOVA with salinity as
the only response there was no significant variation by date or by site. On a separate
28
ANOVA with air temperature as only response there was significant variation by date
only. There was no significant variation in wind speed. On a separate ANOVA with
water temperature as only response there was significant variation by both date and
site. Variations, observed in air temperature and water temperature, are likely due to
seasonal changes throughout the year.
Table 7 MANOVA summary model, all abiotic factors considered.
Df Pillai approx. F num Df den Df Pr(>F) DATE 15 2.5489 2.1079 60 72 0.001 SITE 2 0.7713 2.5109 8 32 0.030
29
CHAPTER 4: DISCUSSION
Number and Size of Oysters A significant interaction between all factors indicates the amount of oysters and
size of oysters present were both dependent on which site they were deployed, what
time of year they were sampled, treatment, and where the reef was placed within the
site (Figures 8-13). Scout Island is further south in Brevard County than both Nicol Park
and Marsh Harbor, which may have resulted in natural recruitment only occurring at
Scout Island. Scout Island is also the only location with known natural oyster reefs
nearby and is in close proximity to an inlet, which may lead to greater tide changes
(Melinda Donnelly, pers. comm.). The presence of natural recruitment resulted in a
higher number of small oysters at Scout Island. Lack of recruitment resulted in larger,
surviving gardened oysters at Nicol Park and Marsh Harbor. Certain reefs at all three
sites experienced high sediment deposition, which may have smothered live oysters
resulting in varying levels of success by reef. Predation of oysters on pilot reefs may
have caused variation in number of oysters present. The fall gardened adult oyster
treatment was deployed in November 2014 and thus exposed to conditions at each site
5 months longer than all other treatments, which may have contributed to differences in
number of oysters found on each treatment.
All live oysters found on the blank shell bag treatment (Scout Island only) were
naturally recruited and therefore younger than the adult gardened oysters, which were
raised for 6-9 months prior to deployment. This difference in age also suggests the
30
oysters were different in size, adult oysters being larger than the newly, naturally
recruited oysters. Certain reefs at Scout Island, depending on their within-site location,
received higher amounts of natural recruitment; thus, reefs with higher amounts natural
recruitment have a higher number of small oysters. This may explain the highly
significant interaction between treatment and reef when analyzing oyster size.
Success of each individual reef replicate was highly dependent on the reef’s
location within a site. Different reef replicates of the same treatment had a significantly
different number of oysters at one given sample time. This could have been caused by
water level fluctuations that took place at each site between the months of February and
October of 2015. Many of the pilot reefs were completely exposed and out of the water
during this time frame. This can be seen when comparing water temperatures and air
temperatures at each site (Table 6). Since temperature loggers were zip-tied to an
oyster bag on a reef, when the reefs were exposed the recorded air and water
temperatures only varied by ~5°C or less. From June 2015-August 2015 mean monthly
water temperatures recorded ranged from 29.6°-31.7° C, which closely resemble the
recorded air temperatures for those same months which range from 29°-35° C. The
eastern oyster can tolerate a wide temperature range, but can only be exposed on the
extreme ends of the range for small periods of time. Once exposed to temperatures at
their limit, oxygen demand overweighs its supply, resulting in compromised health of the
oysters (Lannig et al. 2006). It has been stated that temperature has the greatest effect
on oyster health and growth since it has a direct influence on the oyster’s physiological
31
processes (Heilmayer et al. 2008, Lannig et al. 2006). Being out of the water for
extended periods of time and exposed to extreme temperatures during the summer
months in Florida may have hindered the reintroduced oysters’ ability to survive on
some of the pilot reef replicates.
Live Oyster Weight A comparison of final weight and initial weight resulted in a significant interaction
between site, treatment and reef (Table 4). Results show that oyster mass changes by
county-wide location (site), when it was deployed, if it started with live oysters
(treatment), and placement within the site (reef); therefore, all spatial scales seem to be
influencing site specific variation in total mass of live oysters present. Live oyster weight
was indicative of the number of live oysters present and the size of oysters present.
Therefore, bigger oysters and higher numbers of oysters present both result in a greater
total live oyster weight per bag. Scout Island had significantly higher mean total weights
per bag, which is expected since this site also had highest number of live oysters
(Figure 14). At Scout Island, reefs 2 and 3 of the blank shell bag treatment received
more natural recruitment than reef 1, which resulted in more oysters and thus greater
weights in the bags on those reefs. At Nicol Park, fall and spring adult gardened oyster
treatments both decreased in number of live oysters over time and thus their final
weights are significantly lower than their initial weights. Lack of recruitment at Nicol
Park, resulting in a total oyster mass of zero for all blank shell bag reefs at that site, may
have influenced the significance of the overall interaction.
32
Natural Recruitment Amount of natural recruitment and size of naturally recruited oysters on the restoration
mat and blank shell bag treatments at Scout Island showed a significant interaction
between treatment and reef (Table 5). This indicates that micro-location of the reef and
whether it was a mat or a shell bag determined the number and size of recruited oysters
present. All oyster restoration mats had under 200 oyster present, whereas reefs 2 and
3 of the blank shell bag treatment had over 500 oysters (Figure 15). Both reefs 2 and
reef 3 of the blank shell bag treatment had over 1,000 naturally recruited oysters in
summer 2015. However, reef 1 of the blank shell bag treatment never had over 200
oysters, further supporting the result that micro-location determined the amount of
recruitment. Another reason for a much higher number of naturally recruited oysters on
the blank shell bag treatment versus the oyster mats is that shell bags provided more
surface area available for the oyster larvae to settle on. While restoration mats contain
approximately 36 shells per mat, shell bags contain approximately 288; this is an 8x
increase in available settlement area. On a separate ANOVA with number of live
oysters as the only response, there was a significant interaction between date,
treatment, and reef. This indicates that not only does number of oysters vary by
treatment and by reef, but also over time the amount of oysters is changing. This could
be due to intraspecific competition of resources, such as food and space, among the
newly recruited oysters. Interestingly, on a separate test with oyster size as the only
response, there was were no significant differences or interactions between factors.
33
This leads us to believe that while the amount of naturally recruited oysters is changing
over time, the oysters aren’t necessarily surviving and growing.
Abiotic Factors For abiotic factors there was significant variation by site and by date (Tables 6, 7). On a
separate ANOVA with salinity as the only response, there was no significant variation.
This suggests that although the three sites are spread out from north to south in
Brevard County their salinities were similar and it is unlikely that salinity played a role in
oyster survival or recruitment. On a separate test with air temperature as the only
response there was significant variation by date only, which is expected as temperature
changes throughout different the seasons. On a separate test with water temperature as
the only response, significant variation in date and site suggests that the water
temperatures vary by season and by their latitudinal position in Brevard County.
Restoration Implications So far, we have determined that location is the greatest influence on the survival
and natural recruitment of oysters on the pilot reefs. More importantly, within-site
location was very important for gardened oyster survival and natural recruitment. These
results will allow us to determine the best methods for placing eastern oysters in new
locations of the Indian River Lagoon. In areas with no recruitment and limited gardened
oyster survival, regular gardened oyster replacement will be needed to maintain
populations. In areas with natural recruitment, blank shell treatments were successful.
Due to variable success within treatment replicates, new restoration sites should be
tested prior to any large-scale deployments. With further research, scientists may be
34
able to narrow down other influences, abiotic & biotic, at each location that may hinder
or aid in the success of reintroduced oysters. It is highly suggested that annual water
fluctuations and natural recruitment potential be taken into consideration prior to
deployments. Success of these pilot oyster reefs will allow us to consider future
deployments as a natural method to improve water quality. Results from this study
provide methods that scientists may be able to use in other shallow-water estuaries to
reintroduce oysters to improve water quality.
35
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